I got this tip from my husband who's now doing his second Master's.
When you print off your essay, you see things that you just don't notice on a screen.
Another tip he gives is to read your essay aloud.
And get someone else to read it - they don't have to be high-level. In fact, your writing should be clear enough to follow even if your reader does not speak English well (you may need to explain a few words but the point is this - can they follow and understand the arguments and the logic of what you're saying?)
Try it and let me know if it helps.